1. Field Of The Invention
The invention relates to means for controlling algae and other biological growth in the weir of a clarifier of waste water system.
2. Background Art
Sewage systems are physical systems for the collection of waste water and its treatment before discharge back into the environment. Domestic waste water includes the used water of businesses, office buildings and dwellings.
Chlorine and its compounds (e.g., calcium hypochlorite) are extensively used for disinfecting municipal and other domestic water supplies.
Common treatment facilities for treatment of raw waste (sewage) water from a pumping system has the successive steps of grit removal, preliminary sedimentation, final sedimentation and sludge treatment. Sometimes between the sedimentation steps an aeration step is used. Chlorine treatment to the flow prior to the preliminary sedimentation is often used to minimize odors from the sedimentation tanks. Chlorine treatment of the final effluent from the final sedimentation tank is also often used to disinfect the final effluent.
The purpose of the preliminary and final sedimentation tanks is to separate solids (sludge) from the waste water. Sedimentation tanks often are single-compartment thickeners or clarifiers, typically Dorr clarifiers of which there are two main types, namely, circular and square. The two main types of Dorr clarifiers have certain common and essential features, namely: a shallow symmetrical concrete tank; provision for introducing the feed, overflowing the clarified liquor, and discharging the thickened sludge; and a motor-driven revolving mechanism for sweeping the settled solids to a central discharge hopper in the bottom of the tank. Positive removal of sludge is effected by a diaphragm, plunger or other types of pumps. Skimming devices can be furnished, if desired, for continuously removing scum and other light material that tends to float on the surface.
With the Dorr clarifier installed in circular tanks, feed enters centrally below the water level through suitable connections, terminating in a slotted cylindrical diffuser. The central column, supporting the revolving mechanism, and the central drum form a conduit for the influent. The feed leaves the central drum in a radial direction through slots. The head of water above the slots and the circular baffle have the effect of tapering the velocity of flow and giving quiescent feed conditions. Distribution continues throughout the tank on the same radial diverging lines. The rates of diffusion is gradually decelerated as the circle of propagation increases, so that the velocity reaches the absolute minimum as the flow approaches the side of the tank. A continuous annular trough with a continuous weir on its inboard side extends around the complete periphery of the tank. This gives maximum trough and weir length for any tank of equivalent capacity and assures minimum velocity of flow at the point of take-off. A circular scum baffle may be provided just inside the weir. The clarifier mechanism consists of two radial trussed arms, driven by a motor on the stationary central column, and equipped with plough blades that just clear the bottom and sweep settled solids to the central discharge hopper in the bottom. The rake arms are attached to a central drum, concentric with the central column. Sludge is removed continuously by a diaphragm pump. Where scum and floating solids tend to accumulate on the surface of the tank, positive mechanical means are provided for its removal.
The Dorr clarifier installed in square sedimentation tanks follows closely the arrangement of the Dorr circular-tank clarifier with the exception that the tank is square, not round, and one of the rigid arms of the clarifier mechanism is equipped with a special corner blade that reaches out into the four corners of the tank and moves the settled sludge in to the point where it may be picked up by the regular mechanism. The action of the corner blade is positive and controlled automatically. Every square foot of the tank bottom is swept at each revolution of the mechanism. Feed enters centrally through suitable connections, is distributed radially by a submerged diffuser, and is collected peripherally across a continuous weir extending around the four sides of the tank. Two radial arms with plow blades attached are secured to a central revolving drum and are driven by a gear motor mounted on top of the center pier. These revolving rake arms sweep the area of a circle inscribed within the square bottom of the tank. A diaphragm or plunger pump is used for sludge removal and for control purposes. Scum-skimming devices of several different types are supplied to meet different conditions.
It is an ongoing problem to rid the weirs and outfall surfaces of clarifiers for waste water of algae or other biological growth that build up on these areas due to normal usage. The most used methods of removing these algae include taking the unit out of service to stop flow while being cleaned. This act limits the capacity of the treatment facility while hand dispersing calcium hypochlorite to the surfaces and scrubbing clean with a wire or Teflon bristled brush. This prior art method requires numerous man hours of labor intensive effort while being exposed to the effects of calcium hypochlorite.